Most likely: riboflavin (vitamin B2).
Beef liver is rich in B vitamins, and riboflavin can make urine look extra yellow or even neon yellow when the excess gets excreted. That is usually expected and not a cause for alarm by itself.
Also, dehydration can make urine darker/more concentrated, so if you ate liver and were a bit dry, the yellow can look even stronger.
Get checked sooner if the urine is dark brown/tea-colored, red, cloudy, painful/burning, foul-smelling, or if you also have yellow eyes/skin, fever, or abdominal pain, because those patterns can point to something other than vitamins.
So: bright yellow after beef liver = usually just B vitamins, especially B2.